The present invention relates to flow control valves.
In many control embodiments it is necessary to provide fine control of the flow rate through a valve. This is often accomplished by a flow control valve. Flow control valves generally modulate the flow through a controlled aperture. For example, in one common design the valve has a small orifice with a tapered seat and a needle shaped plunger that is controllably adjusted into and out of the seat to finely control the size of the valve aperture and flow rate. The finely controlled movement of the needle into or out of the aperture permits fine adjustment of the amount of flow through the valve.
While needle valves are often used for flow control applications, unfortunately they are susceptible to wear when in use as a result of the constant flow of fluid through a narrow aperture that may also be subjected to substantial pressure drops. The controlled fluid flow tends to create mechanical vibrations which fatigue the needle, and/or wear and enlarge channels within the valve seat or needle, both of which prematurely age the valve. Due to the tight tolerances required for accurate flow control, a worn needle or valve seat typically requires replacement of the entire needle valve rather than repair with replacement parts.
It has been known to form valves using ceramic discs as valve elements. Ceramic valves have the advantage that the ceramic surfaces can be made very flat and thus form a seal based on Van der Waals force without the need for a gasket or other wear part. However, ceramic valves have thus far found only limited use. One exemplary use of ceramic in valves is a distribution valve, having two rotary ceramic elements, one of which carries a channel and the other of which includes an array of ports to which the channel can be selectively connected based upon the relative positioning of the discs. The ceramic disc surfaces are highly planar, having been ground and/or polished during manufacture, and are able to provide an operational seal for the valve which allows sliding of the discs relative to each other. By sliding (for example, rotating) the discs relative to each other to a chosen location, flow can be directed to a desired one of the ports.
US Patent Publication 2017-0204977 discloses a ceramic disc valve for modulating the flow of fluid. A fixed disk includes an aperture which can be covered by a movable disc to close the valve, or the movable disc may be shifted from over the aperture to permit fluid flow. The fixed disc includes an aperture which is described as potentially circular, rectangular, elliptical, or triangular in cross section, which is covered or uncovered by the circular cross section of the movable disc as it slides across the fixed disk. The '977 application indicates this device may be use to modulate the flow of fuel to a fuel cell by controlled flow through the opening created between the movable disc and the circular, rectangular, elliptical or triangular aperture in the fixed disc.